The objective of Project 3 is to ascertain how exercise training, in combination with favorable genotypes, affects blood pressure (BP) reactivity to an acute laboratory challenge and development of measures of preclinical essential hypertension (EH). Project 3 will focus primarily on the endothelial system (ES) as a mechanistic vasoactive biological pathway, but will also include measures from the sympathetic nervous system (SNS) and the renin angiotensin aldosterone system (RAAS). Project 3 will study a cohort of 150 African American (AA) girls and 150 AA boys aged 8-11 years who will be randomized to a 10-month exercise training intervention or control group. Testing will occur at months 0, 5 and 10. Measures will include vasoactive mediators, epinephrine/norepinephrine and BP at rest and in response to an acute behavioral challenge, endotheliumdependent arterial dilation to reactive hyperemia (EDAD), arterial stiffness, micro albumin (micronALB), left ventricular mass (LVM), body composition, cardiovascular fitness, psychosocial factors and free-living physical activity and diet. Five candidate genes affecting BP through the ES will be genotyped. The specific aims of Project 3 are to test the hypotheses that exercise training will lead to improvements in endothelial function and BP at rest and in response to a laboratory challenge through increased nitric oxide (NO, measured via NO metabolites [NOx]), decreased endothelin-1 (ET-1), and improved vascular remodeling. In addition, gene-environment interactions will explain some of the inter-individual variability in these responses. Possible moderating influences of sex, psychosocial factors, and lifestyle factors will also be examined. The long term objectives of Project 3 are to improve the understanding of the way exercise training may reduce the risk of development of EH. Findings from the present study may lead to more effective primary prevention programs involving exercise training interventions, taking into account potential genetic predisposition to a more favorable response to such an intervention, particularly in individuals at higher risk of developing EH.